Among various types of iron oxide hydroxide (FeOOH) with different crystalline states, amorphous iron oxide hydroxide is an initial state for crystalline iron oxide hydroxide (α, β, or γ-FeOOH), and has a crystalline aggregate smaller than 5 nm, and the structure is ordered in short range and disordered in long range. Such a structure allows amorphous iron oxide hydroxide to have relatively high desulfurization activity.
The applicant has been committed to desulfurization property study of amorphous iron oxide hydroxide and has published an article titled “Preparation and property evaluation of ambient temperature desulfurizer iron oxide hydroxide” (referring to pages 68-71, National Information Center of Gas Purification, Proceedings on Technical Seminar, 2010). This article discloses a laboratory preparation thought of amorphous iron oxide hydroxide, and verifies the desulfurization and regeneration mechanism of the amorphous iron oxide hydroxide through experimental data. However, this study is still at the laboratory exploration stage, and the final objective of this study is to achieve a mass production of amorphous iron oxide hydroxide with high purity and high sulfur capacity in industrial production.
However, so far, amorphous iron oxide hydroxide desulfurizer is not commonly used in practice. The so-called amorphous iron oxide hydroxide desulfurizers sold in the market have poor desulfurization property and are difficult to be regenerated due to low purity of amorphous iron oxide hydroxide (lower than 40%) and high content of other non-regenerative iron oxides (ferroferric oxide, ferric oxide or iron oxide hydroxide in other crystalline states).
In prior art, a reference titled “Research on desulfurization activity of iron oxyhydroxide prepared with different alkali ratios” was published on Coal Science and Technology, Vol. 34 No. 10, October of 2006. This reference provides a preparation method of amorphous iron oxide hydroxide, which comprises following steps: A certain amount of distilled water and ferrous salt are added into a reactor and stirred, and nitrogen is passed into the reactor for protection. After the ferrous salt is dissolved, according to an alkali ratio of 1, a certain amount of alkali solution is dropped into. After the alkali solution dropping is finished, nitrogen is replaced with air for oxidation reaction, and when the conversion rate of [Fe3+]/[ΣFe] reaches 100% and when the color of the solution observed by paper chromatography does not change further, the oxidation reaction is finished. The sample is washed to remove Na+ contained therein, obtaining a filter cake of amorphous iron oxide hydroxide. The amorphous iron oxide hydroxide prepared under the above mentioned conditions has low purity, and contains a large amount of iron oxides and iron oxide hydroxide in other crystalline states, which results in low purity, low sulfur capacity and non-regenerative characteristic when the generated amorphous iron oxide hydroxide is used as a desulfurizer. The reasons for these problems are that, the preparation of amorphous iron oxide hydroxide is strongly influenced by preparation conditions such as pH value, temperature, feeding speed and so on, and small changes on preparation conditions will result in big difference on contents of amorphous iron oxide hydroxide, iron oxides and iron oxide hydroxide in other crystalline states. Therefore, it is very difficult to explore preparation conditions which allow preparation of amorphous iron oxide hydroxide with high purity and high sulfur capacity.
The preparation method of amorphous iron oxide hydroxide disclosed by the above mentioned reference is also a laboratory method, which needs nitrogen protection and has a complex preparation process and a high production cost, so is not applicable to industrial production.